Manufacture of spark plugs



Dec.` 19, 1933.` H RABEzzANA MANUFACTURE oF SPARK PLUGS Filed sept. 19, 195o I gmnto'a Patented Dec. 19, 1933 g 1,941,1324IN e PATENT OFFICE MANUFACTURE oF SPARK PLUGS Hector Rabezzana, Flint, Mich., assigner to A C Spark Plug Company, Flint, Mich., a company of Michigan Application September 19, 1930 Serial No. 483,002

8 Claims.

This invention relates to spark plugs and their manufacture.

It is among the objects of the invention to provide an improved spark plug of simplified construction which will reduce cost of manufacture, automatically provide for a proper predetermined amount of clearance at the spark gap upon assembly of the parts and present a large area of surface at the spark gap so as to afford long life to the electrodes and eliminate the need for frequent regapping during use.

`Various other features of ,advantage will be come apparent during the course of the following specification, having reference to the accompanying drawing of a preferred embodiment and wherein Figure 1 is a detailed sectional view illustrating a spark plug shell at one step in the manufacturing process.

Figure 2 is a section on line 2-2 of Figure 1. Figure .3 is a view similar to Figure 1 of the spark plug shell in a completed stage and ready,

for the final assembly operation.

Figure 4 is an elevation, partly in section, of an assembled spark plug made according to the present invention. i

Figure 5 is a bottom plan View of the plug shown in Figure 4 and Figure 6 is a part sectionalview to illustrate a slight modification.

Referring to the drawing, there is shown in Figure 4 what is commonly termed a two-piece mica plug which is particularly adaptable for use in heavy duty and high-speed, high-compres sion engines such as are used in airplanes and racing vehicles. The inner piece or center assembly encloses a central electrode or wire having 'an enlarged head 1 at its lower end and a terminal connector 2 at its upper end by means of which the usual electrical connection with the ignition wiring may be made. The intermediate part of the electrode is enclosed within a tube or sleeve 3 of mica wrapping surrounding which tube at the central point is a collar or sleeve 4 preferably of copper, brass or other ductile metal, carried by and enclosed within the nut 5, whicli is exteriorly screw-threaded, as at 6. Interposed between the nut 6 and the head l of the electrode are a series of mica washers or discs 7 and between the nut 6 and terminal 2 are a similar set of mica lamin 8. The parts thus far described comprise the central piece, the assembly of which may include the heating and collapsing of a portion of the nut 5 to contract the collar 4 and thereby hold the mica tube 3 tightly about the central electrode as is more particularly described in one of my co-pending applications.

This center assembly is removably secured in the screw-threaded upper endY -9 of the outer shell 10, the skirt portion l1 of which is exteriorly 33 screw-threaded for engagement in the customary spark plug opening of the engine block to position in the combustion chamber the spark gap afforded by the head 1 and electrodes 12 carried by the shell. The electrodes 12 may be C5 inserted through the wall of the shell at its lower end in spaced parallel relation, as shown in Figures 1 and 2, andthen welded or otherwise secured in position. At the back of each electrode there is shown an opening or hole 13 through the 70 wall of the shell for the insertion of a gapping tool in the event it should ever become necessary to bend the electrodes inwardly to vary the spacing of the spark gap.

These electrodes are initially of round section wire but after they are once secured in the shell their adjacent sides are cut away according to the present invention, as shown in Figures 3 and 5, to provide an annular groove or notch 14 for cooperation with `the sparking head 1 and thus 80 present a large area of surface at the sparking point which reduces wear and corrosion. Such notches or arcuate grooves are preferably cut to a given depth on an axis coincident with that of the screw threads 9. Likewise, the head 1 is 85x dressed or turned down to a predetermined diameter in a manner to maintain its peripheral surface concentric to that of the screw threads 6 on the nut 5. For this reason, a predetermined spacing of the sparking surfaces will be automatically brought about at the final assembly operation upon the inter-engagement of the cooperating screw-threaded portions 6 and 9 of the respective sub-assemblies, since the sparking surfaces of the electrodes have been machined about corresponding axes. There is eliminated 'therefore,the need for any initial gapping prior to use and the arrangement greatly facilitates vlarge quantity production through the standardization 'and interchangeability of parts. Because 100 of the large area of sparking surface there will be little or no necessity for regapping after the plug goes into use.

.` Figure 6 illustrates a slight modification of the parts in that the side wires 16 are closer together 105 and the head 17 of the electrode is provided with a projection or boss 18 of reduced diameter to extend between the electrode wires. These sparking points, however, are machined in the same fashion as before described, the particular plug shown 1'10 being adapted for an engine having different characteristics from that for which the plug of Figure 4 is intended. Obviously, the invention is not limited to exact details herein shown and various modications of the parts described may be readily made.

Iclaim:

1. In the manufacture of spark plugs of the type wherein an outer shell having a pair of spaced electrodes screw threadedly receives an inner assembly having an electrode for projection between the spaced electrodes, the method of insuring a certain predetermined spacing of the inner and outer electrodes which includes the machining of arcuate grooves in adjacent sides of the shell electrodes on an axis concentric to that of the screw threads in the shell and the machining of a cylindrical peripheral surface on the other electrode on an axis concentric to that of the threads on the inner assembly, and then threading the inner assembly in the shell.

2. In the manufacture of spark plugs of the type which comprise an inner assembly embodying a central electrode and having a portion removably engageable with a similar portion of an outer shell assembly having an electrode portion for co-operation with said central electrode to form a spark gap, the method of insuring a given spacing of the spark gap, which includes the machining of the electrode surfaces in a definite relation to the interengageable portions of the respective inner and outer assemblies, and then locating the inner assembly in the outer assembly with their interengaged portions in engagement. i

3. The method of manufacturing spark plugs of the type wherein an outer shell screw threadedly receives an inner assembly having an electrode, 'which includes machining to a given size a curved surface on the electrode of the inner assembly about an axis coincident to the axis of the screw threads on the inner assembly, machining a curved surface on a part associated with the outer shell and about an axis coincident to the axis of the screw threads on the shell and then threading together the outer shell and the inner assembly to bring said curved surfaces into concentric and predetermined spaced relation whereby automatically to afford a spark gap of a given size.

4. In the manufacture of spark plugs of the type having inner and outer -assemblies screw` electrode .in definite relation to ne screw threads of the inner assembly. V

5. In the manufacture of spark plugs of the type having inner and outer assemblies screw threadedly engaged with each other, the method of providing the desired spacing between inner and outer electrodes automatically at the time the threaded assemblies are interengaged, including working the sparking surfaces of the electrodes to present the same in given relation to the threads of the respective assemblies prior to the interengagement of the assemblies.

6. In the manufacture of spark plugs of the type having inner and cuter assemblies screw threadedly engaged with each other, the method of providing the desired spacing between inner and outer electrodes automatically at the time the threaded assemblies are interengaged, including the machining prior to nal assembly of the screw threads and the electrode of the outer assembly to establish a given relation therebetween and also the screw threads and electrode of the inner assembly in given relation to each other.

7. In the manufacture of spark plugs of the type comprising an outer assembly carrying an electrode and screw threadedly receiving an inner assembly including an electrode, the method of providing a predetermined spacing between the' sparking surfaces of the electrodes when the assemblies are threaded together, which includes assembling the inner assembly with an electrode head having an initial excess of material, dressing said electrode head of the assembly to a predetermined size and shape and in given relation to the screw threads carried by the assembly, and also assembling the outer assembly including the mounting of an electrode wire which initially carries an excess of material, then dressing the wire to a predetermined shape in relation to the screw threads ot its assembly.

8. In the manufacture of spark plugs of the type comprising an outer assembly carrying an electrode and screw threadedly receiving an inner assembly including an electrode, the method of providing` a predetermined spacing between the sparking surfaces of the electrodes when the assemblies are threaded together, which includes providing the sparking head of a central electrode with an initial excess of material, assembling said electrode as a unitary part of the inner assembly, then removing the excess material on the head to bring the sparking surface `thereof into given relation with the screw threads of the inner assembly, providing a side electrode with an initial excess material, assembling it in the outer assembly and then removing the excess material from the side electrode to present its sparking surface in given relation to the screw threads of the outer assembly.

. HECTOR RABEZZANA. 

